Field of the Invention
The present invention relates to an image processing apparatus and image processing method and, more particularly, to a video display technique.
Description of the Related Art
Recently, video display apparatuses such as TV receivers and PC monitors including various display devices, for example, liquid crystal display devices have been put into practical use. A video display apparatus receives video signals of different color components such as R, G, and B signals, performs color adjustment processing such as white balance control and contrast adjustment and various kinds of filtering processing on the video signals, and outputs the processed video signals to a display device, thereby displaying an image.
Typical methods of the filtering processing are temporal spatial frequency separation processing and edge enhancement processing. The “temporal spatial frequency separation processing” is a method which, when dividing the frame period of an input video signal into a plurality of subframe periods, localizes a spatial high-frequency component of a video extracted by using a Gaussian filter or the like into one subframe, and outputs the subframe. This method can reduce a motion blur which is visually recognized in a hold type display device such as a liquid crystal display device.
The “edge enhancement processing” is a process of extracting an edge component by using a differential operation such as Laplacian for each color component of an input video signal, and adds or subtracts the edge component to or from the original video signal, thereby sharpening the video.
On the other hand, when the edge enhancement processing is performed on each color component, a given specific color component is sometimes enhanced more than others depending on the color component balance of a video signal, and as a consequence the tint changes. This phenomenon occurs because especially when a specific color component of a video signal is close to a maximum signal level or minimum signal level, the amount of enhancement of the specific color component is restricted by the output dynamic range, and this makes the tint change conspicuous.
Also, maximum signal levels of R, G, and B defined as white levels are sometimes changed in pre-processing of the edge enhancement processing. Examples are a case in which the tint of the white level is adjusted in white balance control, and a case in which a maximum or minimum signal level which R, G, and B can take is changed in brightness adjustment. The tint changes when the edge enhancement processing is performed on a video signal having undergone this pre-processing for each color component. On the other hand, the brightness is sometimes visually recognized as it has changed beyond the maximum or minimum signal level defined in the pre-processing.
By contrast, a technique which suppresses a change in hue by calculating an amount of enhancement for each color component and applying an amount of enhancement having a minimum absolute value to each color component is known (Japanese Patent Laid-Open No. 2002-150283).
The technique described in Japanese Patent Laid-Open No. 2002-150283 can suppress a change in tint caused by the filtering processing, but the brightness sometimes changes by exceeding the maximum or minimum signal level defined in the pre-processing.
Accordingly, it is necessary to suppress the change in tint caused by the filtering processing, and suppress the change in brightness of the white level caused when the signal level becomes higher than the maximum signal level defined in the pre-processing. It is also necessary to suppress the change in brightness of the black level caused when the signal level becomes lower than the minimum signal level.